// --- 对象属性链影响隐式绑定
function sayHi2() {
    console.log('Hello,', this.name);
}
var person2 = {
    name: 'Christina',
    sayHi2: sayHi2
}
var person1 = {
    name: 'YvetteLau',
    friend: person2
}
person1.friend.sayHi2();   // 属性链最后一层影响隐式绑定